Was there any power steering fluid on the ground after you made the hard
U-turn?
   When I bought my GTP, the power steering made the same noise and it was
low on fluid.  There was never any power steering fluid in the driveway, but
the level kept dropping.
   It turns out that when the lower A-arm bushings got bad, the steering
rack took a beating because it became the more "rigid" link in the
suspension... which pounds the bushings out of the steering rack.
   The fluid leaking out of the ends of the steering rack fills up the
rubber "bellows" on either end of the rack... and gets "squeezed" out when
you turn the wheel all the way to one side or the other.  It doesn't leak
sitting in the driveway... it leaks in parking lots when you turn the wheel
too far.  LOL
   If you start your car up and turn the wheel from lock-to-lock... you
might find fluid pouring down out of the rubber bellows on either end of the
rack.
   Changing the steering rack was absolutely the worst auto-repair job I
have ever done.  Lower the engine/transmission cradle while trying to work
under the car!